The embodiments described herein relate generally to a device used in conjunction with an ultrasonic ablation device and, more specifically, to a transmission member configured to transfer ultrasonic energy to a bodily tissue from an ultrasonic energy source.
Known ultrasonic energy transmission systems are used in many different medical applications, such as, for example, for medical imaging, to disrupt obstructions and/or ablate bodily tissue. In known ultrasonic energy transmission systems for tissue ablation, ultrasonic energy is transferred from an ultrasonic energy source through a transducer horn and then a transmission member, such as a wire, to a distal head. Ultrasonic energy propagates through the transmission member as a periodic wave thereby causing the distal head to vibrate. Such vibrational energy can be used to ablate or otherwise disrupt bodily tissue, for example, a vascular obstruction, a kidney stone or the like. To effectively reach various sites for treatment of intravascular occlusions or regions within the urinary tract, such ultrasonic transmission members often have lengths of about 65 cm or longer.
Known ultrasonic transmission members are constructed to be flexible enough to be passed through various bodily lumens, but also with sufficient strength to transmit ultrasonic energy to the distal tip (e.g., to ablate vascular or urinary obstructions). A stronger, more durable transmission member allows for greater transmission of energy but may not be flexible or thin enough to be advanced through the vasculature to a desired treatment area. A thinner transmission member can be more flexible but is less durable and more susceptible to breakage.
In an attempt to find a balance between strength and flexibility, some known ultrasonic transmission members are tapered along a longitudinal axis of the transmission member such that the diameter of the distal end portion decreases to allow greater flexibility. For example, some known transmission members can include a diameter at the proximal end that is greater than a diameter at a distal end. Moreover, some known transmission members can include a distal tip or “head” that is welded to the reduced diameter section, and which is positioned adjacent the tissue to be treated. Such transmission members can be prone to breakage at or near the distal end of the transmission member where the cross-sectional area of the transmission member becomes smaller and/or at the discontinuous region where the two pieces are joined. Similarly stated, such breakage is generally caused by stress concentration due to transverse vibrations and fatigue. Thus, one difficulty related to transmission of ultrasonic energy through a relatively long transmission member of known design is premature wear and breakage of the transmission member.
Furthermore, the coupling of the distal head to the distal end of the transmission member results in a discontinuity between the transmission member and the distal head due to, for example, weld material, adhesive material, or the like. Such discontinuities can produce reflections of the ultrasonic wave and result in losses of ultrasonic energy. To overcome the energy losses and inefficiency in energy transfer due to reflections or the like, some known systems increase the level of ultrasonic energy transferred through the transmission member. Similarly stated, some known systems apply a high level of energy at the proximal end portion to overcome the inefficiencies of the transmission member (e.g., at the distal end). However, the increase in the ultrasound energy transferred through the transmission member can increase stress on the transmission member and, consequently, can result in premature fatigue and breakage. In addition to the loss of transmission efficiency, known transmission members constructed of multiple pieces are expensive and can be complicated to manufacture.
Thus, a need exists for an improved apparatus and methods for transferring ultrasonic energy from an ultrasonic energy source to a bodily tissue.